This investigation should contribute to an improved understanding of periodontal disease by providing immunochemical information about cell surface antigens which may act as virulence factors for Actinomyces viscosus and A. naeslundii. These bacteria are associated with plaque, root surface caries, and the immunological sensitization of periodontal disease patients, and they also cause periodontal lesions in gnotobiotic rats. Mutants have been isolated which are avirulent for rodents and an initial comparison of virulent and avirulent A. viscosus T14 has revealed a virulence-associated antigen. This antigen and virulence-associated antigens from other Actinomyces will be studied. Cell wall extracts from virulent-avirulent pairs of A. viscosus and A. naeslundii, will be screened by immunoelectrophoresis to detect and compare virulence-associated antigens. The virulence-associated antigen from A. viscosus T14V and from an isolate of A. naeslundii will be purified and studied further. Initial purification attempts will involve chemical cleavage and separation of cell wall polysaccharides from peptidoglycan. Purified antigens will be characterized and compared by their approximate molecular weights, sugar and amino acid compositions, antigenic relationship, and immunodominant groups. Further structural studies might involve the effects of enzymatic and acid hydrolysis on the virulence-associated antigen of A. viscosus T14V. Also purified antigens will be made available for studies of their effects on the functions of lymphoid cells from periodontal disease patients. Finally, homogeneous proteins (lectins and mouse myeloma proteins) will be screened to detect binding activities for Actinomyces cell surface antigens. The identification and characterization of virulence-associated antigens should aid in understanding virulence mechanisms in periodontal disease. A better knowledge of these processes may suggest strategies for the prevention of periodontal disease in man.